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Saturday, November 20, 2010

For Leaky New York Aqueduct, Bypass Tunnel Is Planned by Mireya Navarro - NYTimes.com

Working on the Rondout-West Branch Tunnel of the Delaware Aqueduct in 1942. Cracks have caused flooding in Wawarsing, N.Y., in Ulster County. Photo NYC DEP

New York City plans to build a three-mile-long tunnel to divert water from a leaking aqueduct that carries from the Catskills about half of the city’s drinking water, officials announced on Friday.

The tunnel, to be built under the Hudson River and parts of Dutchess and Orange Counties, will address a problem that has daunted the city since leaks were first discovered in the Delaware Aqueduct in 1988: some 15 million to 35 million gallons of water, coming down from the Catskills, have been escaping daily through cracks.

The tunnel will bypass the worst of two leaks, said Caswell F. Holloway, the city’s environmental commissioner. Construction work is expected to begin in 2013 and be completed by 2019 at a cost of about $1.2 billion, officials with the city’s Department of Environmental Protection said. Officials said that cost, spread out over nine years, was built into the department’s capital program.

For years, the city has faced criticism for its long delays in stanching leaks in two sections of a 45-mile stretch of the aqueduct known as the Rondout-West Branch tunnel, in Orange and Ulster Counties. The cracks in that branch, which was completed in 1944, have caused chronic flooding in the Ulster hamlet of Wawarsing.

New York City officials countered that they faced a challenge in identifying a way to halt the leaks while enabling them to get enough water to the city. Studies of the problem have involved sending robotic vehicles and deep-sea divers into the aqueduct in recent years to inspect and photograph the cracks.

Their plan calls for constructing a bypass tunnel at depths of 600 to 800 feet from Newburgh, in Orange County, under the Hudson to Wappinger, in Dutchess County. The aqueduct will be shut down for eight months to a year beginning in 2018, to allow workers to connect the tunnel in the last phase of the project.

“We’ve settled on a design for a fix, and we’re moving ahead doing that design and taking steps to address the leak,” Mr. Holloway said in an interview.

The leaking portion of the aqueduct would then be sealed and its use discontinued, the officials said.

During the shutdown, engineers will also enter the aqueduct to repair smaller leaks at Wawarsing from inside the tunnel, the officials said.

The 85-mile-long aqueduct, among the world’s largest, is one of two systems bringing water from upstate reservoirs to eight million residents in New York City and another one million people in Orange, Putnam, Ulster and Westchester Counties. The other is the Catskill system.

The shutdown will require lining up other sources for the 500 million gallons of water that the Delaware Aqueduct carries each day from the Rondout Reservoir in the Catskills. About 290 million gallons would come from the New Croton Aqueduct in Westchester County, which is now used only as a backup water source until a filtration plant in the Bronx is completed in 2012.

The city plans to spend another $900 million in water supply projects to make up for the loss of the aqueduct during construction. It has already spent more than $300 million to prepare for long-term repairs of the aqueduct, as well as better monitoring of tunnel conditions and repair methods.

Designed to last at least a century, the aqueduct’s troubled Rondout-West Branch section, which reaches depths of up to 1,200 feet, developed leaks a few decades after its completion. In the Wawarsing area, the tunnel has cracked along a 500-foot stretch. At Roseton, officials said, the cracks run along 5,000 feet.

Mr. Holloway said the leaks had penetrated the tunnel’s concrete lining but were also found in areas where the branch passed through limestone, which is softer and more vulnerable to water corrosion than the harder rock of sandstone and shale found elsewhere in the tunnel’s path.

But the commissioner said monitoring showed that the amount of water leaking had not increased since 2002 and did not pose the risk of an emergency, like a collapse. “We don’t see a substantial risk of this getting worse,” he said.

In a statement on Friday, the Ulster County administrator, Michael P. Hein, called the plan “a real and substantive solution.”

“In light of the hardships being encountered by the residents of Wawarsing, time is clearly of the essence,” he said, adding that the bypass “will not only eliminate the problem for the residents of Wawarsing, it will have profound economic benefit to our area through job creation.”

Paul Gallay, executive director of Riverkeeper, said the plan was a sensible approach. “It’s a big investment in solving a big problem,” he said, adding that the city should also move to compensate homeowners affected by the leaks for damages suffered.

Mr. Holloway said that other solutions, like bypassing the entire Rondout tunnel altogether, had been considered, but that the idea was dismissed as unnecessary.

“We know where the leaks are and why,” he said.

Another possibility was to drain the aqueduct for a longer time to repair it from within, but that raised uncertainty about how long the aqueduct would be out of service.

“You want to know how long the water is going to be off so you know where the supplemental water is going to come from,” Mr. Holloway said, adding, “It’s absolutely critical to get it right.”

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